ART: Some Quick cleanup

Make several fields const in CompilationUnit. May benefit some Mir2Lir
code that repeats tests, and in general immutability is good.

Remove compiler_internals.h and refactor some other headers to reduce
overly broad imports (and thus forced recompiles on changes).

Change-Id: I898405907c68923581373b5981d8a85d2e5d185a
diff --git a/compiler/dex/mir_optimization_test.cc b/compiler/dex/mir_optimization_test.cc
index 362c7fd..199bc27 100644
--- a/compiler/dex/mir_optimization_test.cc
+++ b/compiler/dex/mir_optimization_test.cc
@@ -16,9 +16,10 @@
 
 #include <vector>
 
-#include "compiler_internals.h"
+#include "base/logging.h"
 #include "dataflow_iterator.h"
 #include "dataflow_iterator-inl.h"
+#include "dex/compiler_ir.h"
 #include "dex/mir_field_info.h"
 #include "gtest/gtest.h"
 
@@ -326,7 +327,7 @@
 
   MirOptimizationTest()
       : pool_(),
-        cu_(&pool_),
+        cu_(&pool_, kRuntimeISA, nullptr, nullptr),
         mir_count_(0u),
         mirs_(nullptr),
         code_item_(nullptr) {